The control over selective gene expression throughout development lies partially in the physical state of DNA as it exists in chromatin of eukaryotic organisms. Our knowledge of the structure of chromatin has increased dramatically over about the last four years since the discovery of nucleosomes--the nucleoprotein particles which represent the elementary structural entities of chromatin. Most of this progress has come by concentrating on the uniformity of nucleosomes. However, the evidence is strong that nucleosomes are not homogeneous and that the nucleosomes of transcriptionally active chromatin have an altered conformation. It is now appropriate to study nucleosome heterogeneity and its possible relationship to the functioning of chromatin. I propose to study the involvement of chromosomal proteins in nucleosome heterogeneity in two basic ways: first, by determining if specific chromosomal proteins are associated with "active" and "inactive" chromatin as defined by susceptibility to two endonucleases, DNase I and DNase II. The proteins to be considered are subfractions of histones and of a group of non-histone chromosomal proteins, the HMG's, which have been implicated as structural chromatin proteins. Because these subfractions from wheat can be easily distinguished and isolated, this organism will be used. The second aspect of the study will include use of various techniques, primarily circular dichroism and fluorescence anisotropy, to determine if the above-mentioned proteins function in chromatin by forming specific complexes with one another. Interactions of H2A, H2B, H3, and H4 stabilize the protein core of the nucleosome. If various subsfractions of these histones are involved, the strength of interaction and thus the stability of the nucleosome may be altered. Studies of the possible interactions of H1 subfractions with the HMG's may be especially valuable. Because H1 histones have been implicated in higher order chromatin structure and because there is some knowledge of specific H1-HMG interactions, it is possible that the conformation of "active" chromatin is due in part to specific H1-HMG complexes.